The present invention relates to a method for the preparation of a stabilized catalyst for the polymerization of an olefin. More particularly, the invention relates to an efficient method for the preparation of a stabilized catalyst for the polymerization of an olefin having excellent activity and durability as a catalyst and an advantage that the catalyst can be introduced into the polymerization reactor together with the monomer as a carrier without the troubles of eventual blocking of pipe lines for the introduction of the same.
The catalysts for the polymerization of olefins conventionally and widely used in the prior art are the so-called Ziegler catalysts comprising a titanium halide-containing solid ingredient and an organoaluminum compound. It is known that such a polymerization catalyst can be imparted with increased stability when the catalyst is subjected in advance to a so-called pre-polymerization treatment or a preliminary polymerization by being brought into contact with a small amount of the olefin monomer for which the stabilized catalyst is intended to be used prior to the actual use of the catalyst in the polymerization process so that the amount of a fine powder of the catalyst formed by attritional disintegration can be decreased along with enhancement of the catalytic performance in the activity for the polymerization and stereospecificity of the polymer produced therewith (see, for example, Japanese Patent Publications 49-37835, 52-39781, 54-34714, 57-45244 and 58-1289 and Japanese Patent Kokai 55-123607 and 59-6205).
Since the polymerization catalyst is in an activated state even after the pre-polymerization treatment, however, the catalytic performance thereof is unavoidably unstable in respect of the catalytic activity and stereospecificity of the polymer product even by washing the catalyst with an inert organic solvent such as hexane and heptane so that the catalytic performance is always subject to a gradual decrease in the lapse of time in addition to the problem that, when the catalyst is introduced into the polymerization reactor together with the monomer dissolved in a suitable medium, the pipe line for the introduction is sometimes blocked by the polymer formed in situ.
Recently, Collomb-Ceccarini et al. disclosed in U.S. Pat. No. 4,921,920 that a Ziegler-Natta type catalyst after a pre-polymerization treatment can be stabilized by contacting with a polymerization inhibiting agent such as carbon monoxide or carbon dioxide under a pressure between 0.01 and 1 MPa, for example, at 80.degree. C. for 1 hour. The stabilizing effect obtained thereby is, however, still quite insufficient.